The present invention is concerned with glasses for the fabrication of lenses for optical and/or ophthalmic applications, the glasses having an index of refraction (n.sub.d) between about 1.78-1.82, an Abbe number (.nu..sub.d) greater or equal to 31, and density (.rho.) less than about 3.80 g/cm.sup.3.
For eyeglasses of high correction, the use of a glass having an index of refraction of 1.8 permits, when compared to glasses having lower indices of refraction (1.6-1.7) and of equal correction power, a significant reduction in thickness at the edge (in lenses of negative power) and at the center (in lenses of positive power).
This constitutes an undeniable advantage for the wearer of eyeglasses, particularly in those cases of high corrections (&gt;6 diopters). In other respects, it is known that an increase in the index of refraction is generally accompanied by a degradation of other characteristic properties of a glass; in particular, the density commonly increases. In order that a glass of high index can retain the advantages in comfort mentioned above, it will be necessary that its density not be too high.
Another drawback often associated with an increase in the index is an increase in the dispersion (or a decrease in the Abbe number).